Messages in this thread Patch in this message | | | Subject | Re: [PATCH] sched: Do not bug in __sched_setscheduler() when pi is not used | From | Florian Fainelli <> | Date | Mon, 19 Nov 2018 11:09:50 -0800 |
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On 11/19/18 8:35 AM, Steven Rostedt wrote: > On Mon, 19 Nov 2018 17:24:32 +0100 > Greg KH <gregkh@linuxfoundation.org> wrote: > >> On Mon, Nov 19, 2018 at 10:46:54AM -0500, Steven Rostedt wrote: >>> On Mon, 19 Nov 2018 16:13:11 +0100 >>> Greg KH <gregkh@linuxfoundation.org> wrote: >>> >>>>> Can this patch also be applied to the stable trees? The offending commit >>>>> was first introduced in 4.2. >>>> >>>> What is the git commit id of this patch in Linus's tree? >>> >>> 896bbb2522587e3b8eb2a0d204d43ccc1042a00d >>> >>> The subject was changed when it was applied. >> >> Ah, that helps. >> >> But why is this really needed in the older kernels? You want to crash >> your machine if someone got things wrong? Given that I doubt this is >> being hit anymore, why is it needed in 4.9.y and 4.4.y? > > The problem is that it can crash when people didn't get it wrong (by > using sysrq). > > The bug happened when we combined two functions into one, and where the > BUG_ON() from one was now added to the other function. The one (where > pi is true) requires the function to be called with interrupts > disabled. The other did not have this requirement (and pi happens to be > false). Thus, you can trigger the BUG_ON(in_interrupt()) with a simple > sysrq key stroke, and crash your kernel when it did nothing wrong. > >> >> Also, it doesn't apply there so someone needs to do the backport... >> > > I did the change against v4.2.8 below.
Thanks Steven! Here is the local 4.9 backport:
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 917be221438b..6b3fff6a6437 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4087,8 +4087,8 @@ static int __sched_setscheduler(struct task_struct *p, int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE; struct rq *rq;
- /* may grab non-irq protected spin_locks */ - BUG_ON(in_interrupt()); + /* The pi code expects interrupts enabled */ + BUG_ON(pi && in_interrupt()); recheck: /* double check policy once rq lock held */ if (policy < 0) {
> > -- Steve > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 6776631676e0..b2af7989eb5b 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3682,7 +3682,7 @@ static int __sched_setscheduler(struct task_struct *p, > int reset_on_fork; > > /* may grab non-irq protected spin_locks */ > - BUG_ON(in_interrupt()); > + BUG_ON(pi && in_interrupt()); > recheck: > /* double check policy once rq lock held */ > if (policy < 0) { >
-- Florian
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